In recent years, the interconnection amount of distributed generators DG including photovoltaic power generation to an electric power system is increasing for the purpose of protecting the global environment. On the other hand, a distributed generator DG has a risk of sudden change in power generation due to weather such as clouds and wind. Power companies have a need to know the output of the distributed generator DG frequently, such as at intervals of several seconds, and precisely in order to stably supply electric power.
As a conventional technique, Non-Patent Document 1 discloses a technique for estimating output of a distributed generator DG. The document discloses a method for estimating output of a distributed generator DG by using a power-factor method.
In the estimation of the output of a distributed generator DG by the power factor method, by assuming a coordinate plane in which the abscissa is active power P and the ordinate is reactive power Q, putting plots on the PQ coordinate plane according to the active power P and reactive power Q measured in units of banks of a substation or the like while the distributed generator DG is stopped, and performing, for example, linear approximation processing based on these plots, a load characteristic of the electric power system is specified in advance. This load characteristic is a characteristic when there is no distributed generator in the electric power system.
Next, plots are put on the above active power/reactive power coordinate plane according to real time active power P and reactive power Q (measured, for example, at 10-second intervals) measured in units of banks of the substation or the like. Supposing that the distributed generator DG operates at a power factor of 1, the distributed generator DG outputs only active power. Therefore, when it is assuming that the real-time active power measurement value is P1 and the real-time reactive power measurement value is Q1, the output of the distributed generator DG is calculated by Formula (1).[Mathematical Formula 1]output of distributed generator DG=active power P0 obtained from load characteristic when reactive power is Q1−measured real time active power P1  (1)
The advantage of the power-factor method is that it is possible to calculate the output of the distributed generator DG at that point each time active power and reactive power is measured in units of banks of a substation or the like, and then it is possible to estimate the output of the distributed generator DG frequently.
Measurement of active power and reactive power in units of banks of a substation means that active power and reactive power in an electric-power supplying target area connected via a feeder (distribution line) to the bank. For this reason, the estimation of the power generation amount means to estimate the power generation amount of the distributed generator in units of areas.